1. Field of the Invention
The present technology relates to oil and gas wells. In particular, the present technology relates to a tractor tool for helping to move a bottom hole assembly through a horizontal wellbore.
2. Description of the Related Art
Oil wells are typically examined to determine petrophysical properties related to one or more of the well bore, the reservoir it penetrates, and the adjacent formation. Such an examination is typically carried out by a well logging tool, which is lowered to the bottom of the well, and employs electrical, mechanical, and/or radioactive tools to measure and record certain physical parameters. Lowering the logging tool and other equipment (collectively known as the bottom hole assembly) to the bottom of the well can be difficult, particularly in horizontal or otherwise deviated wells, where tubing is used to push the bottom hole assembly through the well bore. One reason for this difficulty is friction between the bottom hole assembly and walls of the well bore. The result of this friction can be that the bottom hole assembly stops progressing toward the bottom of the well. If the bottom hole assembly becomes stuck, the tubing that pushes the bottom hole assembly can buckle.
One known way to overcome this problem is with a well tractor that applies an urging force to the bottom hole assembly. A well tractor is a wheeled device that may be included with the bottom hole assembly. When the bottom hole assembly is pushed into the horizontal portion of the well, and if the friction between the bottom hole assembly and the well begins to slow or stop the progress of the bottom hole assembly toward the bottom of the well, the wheels on the well tractor may turn to drive the bottom hole assembly further into the well. Use of such a well tractor, however, can be problematic. For example, in reservoirs where the rock has low strength, insufficient traction may exist for the tractor to propel the bottom hole assembly toward the bottom of the hole.